Migrate share activity registration code to ShareHelper

Migrate share activity registration code to ShareHelper

This change migrates some static methods from PrintShareActivity to
ShareHelper.  This is the code the PrintShareActivity relies on to
insert itself into the share sheet.  Offloading this responsibility
to the ShareHelper will allow us to create a generalized ShareActivity
so that we can add multiple activities to the share sheet.

BUG=685856

[iankc, 2017-02-07 23:38:59]

iankc@google.com changed reviewers:
+ cco3@chromium.org, mattreynolds@chromium.org

[cco3, 2017-02-07 23:50:39]

I'd reword the commit message, but other than that, lgtm

Suggestion:
"""
Migrate share activity registration code to ShareHelper

This change migrates some static methods from PrintShareActivity to
ShareHelper.  This is the code the PrintShareActivity relies on to
insert itself into the share sheet.  Offloading this responsibility
to the ShareHelper will allow us to create a generalized ShareActivity
so that we can add multiple activities to the share sheet.
"""

[iankc, 2017-02-07 23:53:11]

Description was changed from

==========
Migrate Component and Thread code to ShareHelper

This change migrates the code the PrintShareActivity relies on to
insert itself into the share intent picker, to the ShareHelper.
Offloading this responsibility to the ShareHelper will allow us to
create a system where we can add multiple activities to the share picker
intent.

BUG=685856
==========

to

==========
Migrate share activity registration code to ShareHelper

This change migrates some static methods from PrintShareActivity to
ShareHelper.  This is the code the PrintShareActivity relies on to
insert itself into the share sheet.  Offloading this responsibility
to the ShareHelper will allow us to create a generalized ShareActivity
so that we can add multiple activities to the share sheet.

BUG=685856
==========

[iankc, 2017-02-08 00:00:30]

iankc@google.com changed reviewers:
+ tedchoc@chromium.org

[iankc, 2017-02-08 00:02:39]

Hello,

We're breaking up a large CL here:

https://codereview.chromium.org/2666833002/

to make it more easy to review. Thanks for your time!

[cco3, 2017-02-08 00:20:33]

Hi Ted, this should be ready to review.  Thanks!

[Ted C, 2017-02-11 00:22:27]

Please create a new class and not put this in ShareHelper.  That class is
already too big and I'd rather not make it any bigger.

Something like:
OptionalShareTargetsManager <or something>

https://codereview.chromium.org/2680983002/diff/20001/chrome/android/java/src...
File chrome/android/java/src/org/chromium/chrome/browser/share/ShareHelper.java
(right):

https://codereview.chromium.org/2680983002/diff/20001/chrome/android/java/src...
chrome/android/java/src/org/chromium/chrome/browser/share/ShareHelper.java:708:
public static void enablePrintShareOption(final Activity activity, final
Runnable callback) {
Don't make this specific to print.  In general, this class shouldn't know
anything about print.

Call it something like:
enableOptionalShareActivities(...)

Then we'll need to pass something like List<Class<? extends Activity>>
shareActivities as a param since we shouldn't hardcode PrintShareActivity below.

And if we have to pass two activity-like params here, let's change the current
activity param to do something like triggeringActivity

https://codereview.chromium.org/2680983002/diff/20001/chrome/android/java/src...
chrome/android/java/src/org/chromium/chrome/browser/share/ShareHelper.java:756:
public static void unregisterActivity(final Activity activity) {
This name doesn't really make sense IMO.  What activity are you unregistering? 
When it was private (and in a much smaller class), I think it was easier to
grok.

Maybe something like:
disableOptionalShareActivities(final Activity triggeringActivity);

Then you'll want javadoc describing the input and that it is the activity that
initially triggered the share (to help differentiate from the share activities
being enabled).

And since you shouldn't know about print, you'll need to keep a List/Set of the
enabled components to disable here.